Infusion pumps are extremely useful medical devices for providing prescribed fluids, drugs, and other therapies to patients. For example, medications such as antibiotics, chemotherapy drugs, and pain relievers are commonly delivered to patients via an infusion pump, as are nutrients and other supplements. Infusion pumps have been used in hospitals, nursing homes, and in other short-term and long-term medical facilities, as well as for in-home care. Infusion pumps can be particularly useful for the delivery of medical therapies requiring an extended period of time for their administration. There are many types of infusion pumps, including large volume, patient-controlled analgesia (PCA), elastomeric, syringe, enteral, and insulin pumps. Infusion pumps are typically useful in various routes of medication delivery, including intravenously, intra-arterially, subcutaneously, intraperitoneally, in close proximity to nerves, and into an intraoperative site, epidural space or subarachnoid space.
A measure of effectiveness of infusion pumps is the startup time, or the length of time between the initiation of an infusion at a user interface of the pump and the moment that the instantaneous delivery rate actually reaches its intended steady state. Infusion pump applications that require precise, and sometimes very small, volumes of fluid to be delivered over rigidly defined durations of time are dependent not only on the ability of the delivery system to accurately achieve and consistently maintain a specific flow rate, but on the aforementioned transition or startup time.
Referring to FIG. 1, traditional infusion pumps can have significant error in delivery during the startup time, which results in safety issues such as under-delivery or over-delivery to the patient. As shown in a traditional infusion pump example of FIG. 1, in which time in minutes is depicted along the x-axis and flow rate in mL/hr is depicted along the y-axis, the actual delivery rate takes over 30 minutes to reach the target delivery rate (steady state). In other embodiments of traditional infusion pumps, this delay can last several hours or more, depending on the type of pump and/or the infusion being delivered. The total startup error of delivery rate deviation can therefore be quite large. As illustrated in the example of FIG. 1, a 0.497 mL error, or nearly 50% underdelivery, exists on a target delivery rate of 1 mL/hr. Clearly, it would be beneficial to clinicians and patients for infusion pumps to reach the target steady state level faster and in a safer manner than current pumps.
A significant factor that contributes to startup time is the drive train or network of mechanical components responsible for transmitting motive force from a motor (or other means of motion generation) to the fluid. Gearing, clutch assemblies, linkage couplings, and manufacturing or assembly tolerances all introduce varying amounts of discontinuity, “slop,” and “lag,” that act to prevent motive force from being rapidly or completely translated into fluid flow. Another important factor of startup time, particularly for syringe-type pumps, pertains to the time that must elapse while the pump's plunger driver increases the force applied to the syringe plunger to the point that the force overcomes opposing forces inherent in the syringe and associated tubing system and thereby begins to generate motion of the fluid therethrough. Each syringe has a “breakout force.” The breakout force is the force required to break or overcome static friction (“stiction”) within, or with respect to, the syringe and begin pumping fluid out of the syringe. Generally, pumps are started at the speed necessary to produce the desired steady state, which the actual delivery rate may eventually reach. Therefore, the aforementioned contributors to startup time are not considered or compensated for. As a result, significant delays in startup time, such as those depicted in FIG. 1 can result.
Traditionally, in order to manage these delays in startup time, a clinician will often initiate or prime a pump in advance of a time when delivery to a patient is needed and simply direct the fluid from the pump into a waste container or sink until the pump begins to visibly pump fluid. Such a method is not only costly and time-consuming, but dangerous to the patient who ultimately may therefore not receive an intended infusion volume.
In another example of managing a delay in startup time, because it may not always be apparent when the infusion pump has reached a steady state, a clinician may check the patient's vital signs in order to determine when the pump has begun pumping fluid. But such an analysis is distinctly disadvantageous, as the patient is being used to determine when the pump has reached a steady state. Such practice clearly raises patient safety concerns, should the pump be programmed with an incorrect rate, or an unintended medication or infusate be unintentionally delivered.
In another example, some pumps physically stop the syringe's plunger or the pump's plunger driver, with a brake or other stopping mechanism, until the detected force exerted by the pump on the syringe plunger exceeds a given running force. At the time the detected force exceeds the running force, the plunger or the pump's plunger driver is released. Such an embodiment can result in not only unneeded wear and tear on the infusion pump and syringe hardware, but in over-delivery to the patient once the particular component is released.
Therefore, there is a need for an infusion pump that reaches the target delivery rate or steady state in minimal time, which minimizes deviation of the delivery rate from the target rate (and minimizes accuracy error by reducing the area under the delivery rate deviation curve of FIG. 1), and allows clinicians to rapidly start pump delivery without priming the pump, employing a brake, relying on patient vital sign data or other analysis, and thereby allowing the clinicians to maintain manageable and efficient workflow practices and focus more on patient care.